Protein kinases are a class of proteins (enzymes) that regulate a variety of cellular functions. This is accomplished by the phosphorylation of specific amino acids on protein substrates resulting in conformational alteration of the substrate protein. The conformational change modulates the activity of the substrate or its ability to interact with other binding partners. The enzyme activity of the protein kinase refers to the rate at which the kinase adds phosphate groups to a substrate. It can be measured, for example, by determining the amount of a substrate that is converted to a product as a function of time. Phosphorylation of a substrate occurs at the active-site of a protein kinase.
Tyrosine kinases are a subset of protein kinases that catalyze the transfer of the terminal phosphate of adenosine triphosphate (ATP) to tyrosine residues on protein substrates. These kinases play an important part in the propagation of growth factor signal transduction that leads to cellular proliferation, differentiation and migration.
For example, the Src family of non-receptor tyrosine kinases has been specifically implicated in cancer cell modulation and growth. See D. H. Boschelli and F. Boschelli, “Small molecule inhibitors of Src family kinases,” Drugs of the Future 2000, 25(7):717–736. Src over expression has been detected in colon, breast, hepatic and pancreatic tumors, as well as in certain B-cell leukemias and lymphomas. Id at 719. Increased Src expression and activity has also been shown to correlate with an increase in tumor malignancy. Id at 719. Thus, Src inhibitors can be useful as antitumor agents.
There are several examples of small molecule inhibitors of protein kinase catalytic activity. In particular, small molecule inhibitors typically block the phosphorylation of substrates by tightly interacting with the protein kinase ATP binding site (or “active site”). See WO 98/24432 and Hennequin L. F. et. al., J. Med. Chem. 2002, 45(6), pp1300. Several of these compounds inhibit multiple targets. For example, W099/61444 (Warner-Lambert) discloses bicyclic pyrimidines and bicyclic 3,4-dihydropyrimidines of formula
that are asserted to inhibit cyclin dependent kinases Cdk1, Cdk2 and Cdk4 as well as the growth factor receptor tyrosine kinase enzymes PDGFR and FGFR. Some compounds are also asserted to inhibit Cdk6.
U.S. Pat. No. 6,150,373 (Hoffmann-La Roche Inc.) discloses bicyclic nitrogen heterocycles of formula
that are stated to inhibit the T-cell tyrosine kinase p56lck.
WO 01/29041 A1 and WO 01/29042 (F. Hoffmann-La Roche AG) disclose alkylamino substituted bicyclic nitrogen heterocycles of formula
that are stated to inhibit p38 mediated cellular functions and are thus inhibitors of cellular proliferation.
WO 01/64679 A1 (SmithKline Beecham) discloses 1,5-disubstituted-3,4-dihydro-1H-pyrimido[4,5-D]pyrimidin-2-one compounds of formula
that are stated to be useful in treating CSBP/P38 kinase mediated diseases.
There continues to be a need for easily synthesized, small-molecule compounds effective in inhibiting the catalytic activity of protein kinases, in particular the Src family of non-receptor tyrosine kinases (“SFKs”), for treating one or more types of cancers, particularly solid tumors. It is preferable that such small molecule inhibitors also possess advantageous bioavailability profiles. It is thus an object of this invention to provide such compounds and pharmaceutical compositions containing these compounds.